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We're Having a Heat Wave...And It's Serious

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The effects of climate change are often portrayed as a future threat, something that will one day bare its ugly (and warm) face and inflict catastrophic damage on our society. This is largely untrue – not the part about the damage, but rather the part about the damage being confined to the future. As a new paper demonstrates in an unusually clear fashion, climate change has already happened, and its effects are rapidly becoming visible in our weather.

The usual refrain when discussing the visible effects of climate change is that no particular weather event can be attributed to human-induced global warming. However, this view is changing, largely as a result of the last several decades' clearly anomalous number of above-average temperature events. Here, the authors show that warming has already shifted the global temperature distribution upward, significantly increasing the frequency of extreme heat waves.

The authors looked at global temperature data between 1950 and 1980. Over this period, the data take the form of a normal distribution, or a bell curve. This tells us that in any given year it is highly likely that the average temperature will fall close to the long-term average, and temperatures farther from the this average are increasingly improbable. This is just common sense; it's extremely unlikely that Chicago will receive snow in July, and just as unlikely that New Year's Day will top 100 degrees.

Given this known temperature distribution, we can determine if a particular time period is above or below normal, by how much, and exactly how unlikely this departure from average is. The authors note that the historical temperature data could be used to determine the areal temperature distribution – the expected percentage of the planet experiencing a certain temperature level at a certain time. For example, temperatures that have a 10 percent chance of occurring according to the historical data should cover, on average, about 10 percent of the planet.

The authors checked whether recent areal temperature distributions matched those predicted by the 1950 to 1980 temperature data. They didn’t; in fact, the recent temperatures were drastically different. From 1980 to the present, the percentage of the planet covered by above-average temperatures has steadily increased, with the most extreme temperatures increasing in coverage at the fastest rate. In 2010, the most unusual heat events – ones which historically had covered only about 0.1 percent of earth’s surface – now covered a rather incredible 13 percent.

According to the historical temperature data, the probability of extreme heat covering such a large portion of the planet is minuscule, and the fact that similar temperatures have been seen relatively consistently for a decade makes it highly improbable that we’ve just hit a spout of bad luck. The authors conclude that the only plausible explanation is that the entire temperature distribution has shifted upwards, so that temperatures that constituted a heat wave between 1950 and 1980 are normal today, and heat events which were once considered extreme are now not all that unusual.

The changes that have occurred may not be obvious to an individual observer, but on a global scale the planet is significantly hotter than it was fifty years ago. Many of the recent extreme heat events have been disastrous. The 2003 European heat wave killed an estimated 70,000 people, the 2010 Russian heat wave cost approximately $15 billion, and the ongoing heat wave and drought in this country is poised to significantly decrease crop yields.

These increasingly frequent heat waves are at best very expensive and at worst very deadly. As this study shows, it does not require an especially technical analysis to observe the effects of climate change – just by comparing today’s temperatures to those of a few decades ago, the changes are quite clear. In a rational world, one would hope that responsible people would react to such information; thus far they have not. Unfortunately, nature will not take pity on humans for their lack of foresight, and the consequences of our inaction will become increasingly severe.

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